1. Field of the Invention
The present invention relates to crystalline metal films.
2. Description of the Related Art
A variety of thin-film formation techniques, including chemical, physical, and combined techniques, have been used in a wide range of industrial fields such as semiconductor materials and magnetic materials.
Thin films can be generally divided into polycrystalline thin films, single-crystal thin films, and amorphous thin films. The most commonly formed thin films of these are polycrystalline thin films, which can be oriented or unoriented, depending on, for example, deposition conditions. An unoriented polycrystalline thin film includes crystal grains randomly oriented so that the orientations thereof are evenly distributed in all directions. An oriented polycrystalline thin film, on the other hand, has the tendency that a particular crystal axis is preferentially aligned in a particular direction.
Crystal structures of thin films can vary depending on, for example, the type of substrate on which the films are formed and temperature conditions. Accordingly, thin films are formed under various conditions selected according to target physical properties.
According to R. Hoogeveen, M. Moske, et al., Thin Solid Films 275 (1996) 203-206, for example, a tetragonal crystal system of tantalum, namely, β-tantalum, is formed if tantalum is deposited on a substrate such as a SiO2 substrate or a BeO substrate, and a cubic crystal system of tantalum, namely, α-tantalum, is formed if tantalum is deposited on an aluminum substrate. According to this document, additionally, heat treatment up to 700° C. is required for substantially complete phase transition from β-tantalum to α-tantalum.